The present disclosure disclosed herein relates to a secondary battery for devices such as a portable electric/electronic device, a hybrid electric vehicle (HEV), and an electric vehicle (EV), and more particularly, to a method and system for rapidly cooling a secondary battery.
Recently, various compact and light electric/electronic devices such as cellular phones, laptop computers, and camcorders are developed and produced. Such portable electric/electronic devices are provided with battery modules for operation without external supply of power. Such a battery module includes at least one battery capable of maintaining its output voltage level greater than a predetermined value for operating an electric/electronic device for a predetermined time period.
Many recent battery modules are constituted by rechargeable second batteries due to economic reasons. Particularly, lithium secondary batteries are widely used in various mobile devices and electronic devices as power sources owing to high energy density, high operating voltage, and long lifespan.
In addition, lithium secondary batteries are receiving considerable attention as energy sources for electric vehicles and hybrid electric vehicles which are alternatives for gasoline vehicles and diesel vehicles causing pollution and global warming due to use of fossil fuel. Some lithium secondary batteries are commercially available for that purpose.
Since lithium secondary batteries have an operating voltage of 3.6 V, which is three times the operating voltage of nickel-cadmium batteries or nickel-hydride batteries that are widely used as power sources of portable electric devices, and have high energy density per unit weight, the use of lithium secondary batteries is rapidly increasing.
Generally, according to the kinds of electrolytes, lithium secondary batteries are classified into a liquid electrolyte type and a polymer electrolyte type. Liquid electrolyte type lithium secondary batteries are called lithium ion secondary batteries, and polymer electrolyte type lithium secondary batteries are called lithium polymer secondary batteries. In addition, secondary batteries can be classified into a cylindrical type, a prismatic type, and a pouch type according to external and internal structures. Since pouch type secondary batteries can have a high stacking density and a narrow width relative to a length and are light, much attention is being paid to pouch type secondary batteries.
Usually, lithium secondary batteries use lithium-containing oxides as positive electrode active materials and carbon materials as negative electrode active materials. For example, a lithium secondary battery includes an electrode assembly, a secondary battery case accommodating the electrode assembly, and an electrolyte injected in the secondary battery case to allow movement of lithium ions. The electrode assembly includes a positive electrode plate coated with a positive electrode active material, a negative electrode plate coated with a negative electrode active material, and a separator disposed between the positive and negative electrode plates to prevent an electric short circuit while allowing movement of lithium ions therethrough. The electrode assembly is formed by winding the positive electrode, the separator, and the negative electrode.
In detail, a positive electrode terminal is connected to the positive electrode plate coated with a positive electrode active material, and a negative electrode terminal is connected to the negative electrode plate coated with a negative electrode active material. That positive electrode plate, the separator, and the negative electrode plate are stacked on one another and are wound to form the electrode assembly.
Then, the electrode assembly is fixedly disposed in the secondary battery case, and the electrolyte is injected into the secondary battery case. After that, the secondary battery case is sealed.
In such battery modules including a plurality of rechargeable unit cells, safety is one of the most important factors. Safety problems of battery modules are caused by heating, external impacts, deterioration of internal components, short circuits, etc.
That is, although a high cell density can be obtained by stacking a plurality of cells, it is difficult to dissipate heat generating from the cells when the cells are charged and discharged. If heat is accumulated due to poor heat dissipation, a significant safety problem may arise as well as deterioration and lifespan reduction of a battery. Particularly, effective heat dissipation is more important for power sources of electric vehicles and hybrid vehicles because such power sources are rapidly charged and discharged and a large amount of heat is generated during a momentary high power operation.
In other words, if heat is not effectively dissipated while unit cells are charged and discharged, heat accumulates to deteriorate the unit cells. In some cases, burning or explosion may arise. Therefore, a cooling system is necessary.
In the related art, a heat sink is attached to one side of a secondary battery including a positive electrode, a separator, and a negative electrode that are stacked many times, so as to absorb and dissipate heat generated from the secondary battery. However, the rate of heat transfer to the heat sink is low because heat is transferred through a plurality of layers of positive electrode/separator/negative electrode. Thus, cooling is not rapidly carried.